In recent years, there is an increasing demand for a lithium ion secondary battery used in mobile information terminals, mobile electronic devices, compact household power storage devices, motor cycles using a motor as a power source, electric cars, hybrid electric cars or the like.
As the method for ensuring safety of a lithium ion secondary battery, an all-solid secondary battery using an inorganic solid electrolyte instead of an organic electrolyte has been studied.
As a solid electrolyte for an all-solid secondary battery, a sulfide-based solid electrolyte obtained by using a sulfide as a raw material has been studied, for example. As the method for producing a sulfide-based solid electrolyte, for example, Patent Documents 1 and 2 disclose that a solid electrolyte is produced by reacting raw materials in N-methyl-2-pyrrolidone or carbon hydroxide. Further, Non-Patent Document 1 states that a solid electrolyte is produced by reacting lithium sulfide and phosphorus pentasulfide in tetrahydrofuran.